REPLACEMENT OF MAINS

摘要

The present invention relates to the replacement of an existing main, particularly an existing cast iron gas main with a new main utilizing a device in the form of a mole. In accordance with the improvement described herein the mole includes a pivotally mounted blade at its forward end and other blades which are fixed. The mole is driven through the existing main by means of a numerically actuated hammer engaged percussively with an internal wall of the mole formed by an internal bore. The pivotal blade pivots under the action of an associated piston which is hydraulically actuated by fluid supplied from a hose by way of a channel. The blade is normally closed but is pivoted to fracture any circumferentially located obstruction located in the main and serving to inhibit the movement of the mole therethrough.